Differences in Grinders
Coffee grinders are divided into two types.
These are the grinders many people are used to and have used before. Blade grinders have two or more blades that rapidly and repeatedly chop the coffee beans into a powder.
Pros - Inexpensive, can be used for other grinding like spices
Cons - High heat transfer, inconsistent, inferior grind
This is an example of a blade grinder.
Burr GrindersA burr mill or burr grinder is a device to grind hard, small food products between two revolving abrasive surfaces separated by a distance usually set by the user. Typically one burr is static (it doesn't move) and the other is rotated by the grinder's motor or in manual grinders the operator's hand. The coarseness is adjusted by bringing the burrs closer together for a finer grind or moving them further apart for a coarser grind. Burr mills do not heat the ground product by friction as much as blade grinders, and produce particles of a uniform size determined by the separation between the grinding surfaces. High end burr grinders are remarkably consistent in the grinds they produce and feature a wide array of settings from coarse to very fine.
Pros - Low heat transfer, consistent, some models come with espresso dosers, fast
Cons - some high end models can be pricey
Here are pictures of two different types of burrs, the first are conical burrs and the second flat burrs.
And here is a close up of two flat burrs.